This invention relates to a process for producing free flowing chromium oxide powders by agglomerating chromium oxide powders with chromium acetate as the binder, sintering, and plasma processing. The resulting powders have less than about 1% by weight free chromium. The powders are suitable for plasma spray applications.
Chromium oxide powders are used in plasma spray applications. Normally this powder is produced by sintering or via arc melting and subsequent crushing. The high temperature sintering and arc melting processes can form free chromium. There is invariably post-heat treatment given to reduce the level of acid soluble constituents from greater than about 1000 weight ppm to less than about 500 weight ppm. If free chromium is present at greater than about 1000 weight ppm the wear properties and corrosion resistance of coatings made of this material are affected. In addition, flow characteristics and yields of the crushed product are often undesirable. Typically the powder is sprayed through a plasma and is used to coat a substrate such as steel. In this type of application the powder must be free-flowing. Spherical particles, due to their free-flowing nature are more desirable than non-spherical particles since they considerably reduce spraying time in a coating application.
Therefore a method to produce such powders that are low in free chromium and free flowing would be highly desirable and an advancement in the art.